1. Field of the Invention
The present invention relates to a self-lighting type push-button input device such as an operating panel of a portable telephone wherein plural push buttons are provided for input and are illuminated for convenience in using the input device in a dark place at night for example.
2. Description of the Related Art
FIG. 11 shows a constructional example of a conventional self-lighting type push-button input device 90. In the input device 90, a part of a push-button 91 and a spring portion 92 are formed using silicone rubber with a light diffusing agent incorporated therein for example, the spring portion 92 are formed using silicone rubber with a light diffusing agent incorporated therein for example, the spring portion 92 being adapted to deflect upon depression of the push-button portion 91 and give a stroke to the push-button portion 91, and a key top portion 93 formed of a transparent or milk-white resin is mounted so as to cover the push-button portion 91.
Further, a light conducting portion 94 formed of a transparent and rigid resin is embedded in the silicone rubber by integral molding at a position in under the push-button 91 and inside the spring portion 92. It is the construction of one push-button 95 that has been described above. In this conventional example, plural push-button units 95 are connected side by side through a base portion 96 formed of the silicone rubber referred to above. A light source 97, e.g., LED lamp, is disposed face to face with the light conducting portion 94 in each in each of the push-button units 95 to effect illumination.
[Patent Literature 1]
Japanese Unexamined Utility Model Publication No. Hei 7 (1995)-10701
In the above conventional push-button input device 90, since the push-button portion 91 is formed using silicone rubber with a light diffusing agent incorporated therein, light is diffused uniformly in the push-button portion 91 and there is obtained a key top surface of uniform brightness, thus affording a product superior in quality impression.
In the conventional push-button input device 90, however, the base portion 96, as a portion other than the push-button 91 for which the diffusion of light is required, is also formed using silicone rubber with a light diffusing agent incorporated therein, so that when light is to be propagated by utilizing the base portion 96, a great propagation loss occurs due to the diffusion. As a result, as noted above, it is required that one light source be provided for each of the push-button units 95, thus giving rise to the problem of an increase of cost.